1. Field of the Invention
The present invention relates to a new and improved emergency brake apparatus for an elevator, especially a traction elevator containing a car, counterweight, hoist ropes, drive sheave, brake, motor, elevator car safety as well as this additional emergency brake which acts directly at the drive sheave.
2. Discussion of the Background and Material Information
An elevator installation of the aforementioned type possesses the previously mentioned elevator car safety in the form of a rail safety which, in the presence of overspeed or excessive velocity of the elevator in the down direction, is tripped by a mechanical velocity limiter. During the running of the elevator, the normal operating brake serves as holding brake and upon response of a contact located in a safety circuit this operating brake can initiate an emergency stop in both travel directions of the elevator.
With the view of satisfying more stringent safety requirements and stricter safety codes which may possibly be enacted in the future, the need exists for an additional brake apparatus which functions independently of prevailing brake apparatuses and becomes active prior to the rail safety. This additional brake apparatus should specifically bring about a controlled and reproducible emergency braking action in the up-travel direction of the elevator. On the one hand, braking of the upward travelling elevator should not exceed a deceleration of 1 "g", but, on the other hand, should allow for a deceleration of, for example, 5 to 7 m/sec.sup.2. The operating brake is unsuited for this purpose, because with driving load, namely, a full car in the down-travel direction and an empty car in the up-travel direction, there is only still possible a deceleration of slightly more than 1 m/sec.sup.2. On the other hand, with the rail safety there are attained decelerations greater than 1 "g", so that such is not used in the up-travel direction because of rope slack and other effects. Additionally, the release of an actuated rail safety is associated with considerable expense, such as typically the need to rework the rails at the engaged location of the safety.
In U.S. Pat. No. 4,923,055, granted May 8, 1990, entitled "Safety Mechanism for Preventing Unintended Motion in Traction Elevators", there is described a solution where brake levers equipped with brake shoes and which are pre-biased by a spring are arranged to both sides of the end faces of the drive sheave. These brake levers together with their brake shoes are laterally pressed by a trigger mechanism against the end faces of the drive sheave, resulting in an appropriate braking action. The triggering action is indirectly accomplished by a solenoid or electromagnet which releases an entrainment lever or trigger which is then engaged and actuated by a radial boss of the drive sheave. Thereafter there is eliminated the mechanical latching of the still open emergency brake and the brake levers engage the drive sheave with a force governed by the pre-biased spring and exert a braking action upon the elevator car. This safety mechanism is designed as a structural addition to the elevator installation and contains many components, and after tripping of the safety mechanism it must be manually reset into its preparatory or ready state.
U.S. Pat. No. 4,977,982, granted Dec. 18, 1990, entitled "Elevator Sheave Brake Safety" and U.S. Pat. No. 5,007,505, granted Apr. 16, 1991, entitled "Elevator Safety", each disclose an emergency brake apparatus wherein brake elements are tangentially guided towards the drive or traction sheave, and apart from a spring pre-bias there comes into play a mechanical servo-action due to the entrainment effect. It is very difficult to reproduce a defined braking torque. Furthermore, both of these prior art emergency brakes are designed as retrofitted structures.